The present invention generally relates to laser instruments and, more particularly, to an optical arrangement in a laser scanner for generating a scan pattern to find and read a bar code which is spaced from the scanner, such as a package label carrying a bar code symbol, wherein enhanced compactness of the optical arrangement minimizes the overall vertical height of the laser scanner.
Bar code symbols are used on a broad range of retail packages for check-out and inventory purposes and a variety of laser scanners have been designed to read such symbols. Little attention has been paid to the physical size of these laser scanners. Instead, the ability to provide high performance scanning has been emphasized without any concern for how tall or large the scanner unit might be. With this latitude in design available to manufacturers, some laser scanners have been made that are as much as 75 cm tall. This lack of emphasis on scanner height has prevented using scanners in some applications where appearance and counter space are important.
Up to the present time, the primary design limitation with respect to overall scanner size has been the space requirements of the various scanner components. It has not previously been possible to include the transmission optics, the collection optics, and the geometry of the scan pattern and the optical components, i.e. mirrors, that create this pattern, into a sufficiently shallow vertical height scanner. One laser scanner has been designed and introduced heretofore by the assignee of the present invention specifically to meet the requirements of reading bar code labels at package speeds up to 100 inches per second in an overall scanner size less than 13 cm tall.
This laser scanner utilizes a retro-directive optical system composed of transmission optics, collection optics and a scan pattern generating arrangement. The transmission optics include a low power He-Ne laser, two small routing mirrors, a diverging lens on the end of the laser, and a focusing lens that is molded as part of a larger collection lens of the collection optics. The basic function of the transmission optics is to create and transmit a focused laser spot, of the correct diameter, at the plane of the package label to illuminate the bars and spaces of a bar code symbol on the label.
The collection optics of this prior art scanner includes a collection lens, a bandpass filter and a photodetector. The basic function of the collection optics is to gather and collect only the diffuse laser light reflected from the label and focus it onto a small detector. The light is collected and focused in such a way as to optimize the signal-to-noise ratio. In the retro-directive optical system of the scanner, a cone of light returning from the label and surrounding the beam of light being transmitted to the label is collected by the collection lens. In this way, a substantial portion of ambient light is eliminated from the system. Additional filtering of ambient light "noise" is achieved by the bandpass filter.
The basic requirement for grocery and other high volume transaction laser scanners is to operate in a way that the store check-out clerk does not have to worry about the label orientation as the product label is passed over the scanner. Pursuant to that requirement, the scan pattern generating arrangement of the prior art laser scanner has employed a multi-faceted mirror assembly consisting of high reflectivity mirror surfaces which spin about a generally horizontal axis. The basic function of the scan pattern generating arrangement is to move the beam of laser light through a three dimensional pattern capable of finding and reading labels in as many orientations as possible.
Although the Model 750 SL laser scanner has provided a high performance, low profile POS scanner design which has met and surpassed European market requirements, it is perceived that further improvements in performance and reduction in scanner height are desired to satisfy the continuing demand for high performance, low cost scanners in specific applications.